F. W. Dry 



91 



It is obvious that the flies of the first brood have to move a greater 

 or less distance to find swedes as it is extremely unusual for swedes to 

 be grown on the same ground in two consecutive years. And I obtained 

 evidence in 1913 that many flies of the second brood did lay their eggs 

 in fields in which they had not spent the pupal stage. Many fields, 

 chiefly late sown ones which missed the first brood altogether, were 

 attacked by the second brood, often having a percentage of infected 



50 



40 



30 



20 



10 



NUMBER OF ROW 



Fig. 6. Graph showing distribution of plants infected by Brood II of the Swede 

 Midge in a late sown 1913 swede field which was not attacked by Brood I, situated near 

 to an earlier sown 1913 swede field which was attacked by Brood I. 



The rows are numbered from the side of the field near to the earlier sown field. 



plants quite high for the year 1913. The following are a few examples 

 taken from a considerable number of such cases: 



District I 

 IX 

 IV 

 VII 

 „ VII 



Date of sowing 

 May, last week 

 June, first week 

 June, second week 

 June, second week 

 June, third week 



Brood I 

 %CL 





 

 

 

 



Brood II 

 %CL 



3 



9 



3 

 10 

 20 



Clear evidence of the actual movement of flies from one particular 

 field, comparatively early sown, to a later sown field, which missed the 

 first brood altogether, is given in the graph, Fig. 6. Here the % CL 



